1. Field of the Invention
The present invention relates to a gas laser oscillating device, and more particularly to an axial-flow type gas laser oscillating device in which the physical axis of the electric discharge tube coincides with the optical axis of the electric discharge tube.
2. Description of the Prior Art
A known conventional gas laser oscillating unit for obtaining a stable laser beam has a construction as shown in FIG. 1.
Referring to FIG. 1, the gas laser oscillating unit is provided with an electric discharge tube B for generating an electric discharge which is used as a laser excitation source for laser gas flowing in a direction shown by an arrow A between metal electrodes of anode and cathode. The cathode C of the metal electrodes is connected to a tube member E by way of a tapered hollow member F having a tapered inner surface f. The tube member E has a slit D enclosed therein for generating a swirl of laser gas upstream of the cathode C. At least the inner surface of each of the tube member E and the tapered hollow member F is made of an alloy material containing aluminum which is processed to form a black anodized aluminum (referred to as "alumite" hereinafter) layer G thereon by processing with an organic dye.
In the above type gas laser oscillating unit, there can be obtained a high-speed gas stream of approximately 100 meters per second in an electric discharge section H inside the electric discharge tube B, where diffused laser beams are efficiently absorbed by the above-mentioned black alumite layer G, resulting in obtaining a stable laser beam and consequently achieving a high-precision of a laser beam machining or the like process.
However, the above conventional construction has a problem that the cathode C and a total reflection mirror I are soiled which results in reducing the laser output as indicated by a broken line in FIG. 4 (to be described later).
According to research made by the inventors of the present invention, when the above-mentioned black alumite layer G continues to absorb diffused laser beams for a long time, the organic substance contained in the organic dye of the black alumite layer G vaporizes into the laser gas to soil the cathode C and the mirror I.